Alexandrov D.,Saint Petersburg State University |
Bakulin A.,Saudi Aramco |
Burnstad R.,Aramco Research Center |
Kashtan B.,Saint Petersburg State University
Geophysics | Year: 2015
Time-lapse surface seismic monitoring typically suffers from different sources of nonrepeatability related to acquisition imperfections as well as due to complexity of the subsurface. Placing sources and receivers below the surface can improve seismic data repeatability. However, it is not always possible to bury a large number of sources, and therefore the next best option is monitoring with surface sources and buried sensors. We have discovered that redatuming of surface sources to the shallow buried receivers produced a reliable image of target reflectors despite the fact that receivers were placed in the near-field zone of the source. We redatumed data with the virtual source method using crosscorrelation of the measured wavefields. We found that redatuming also reduced nonrepeatability of seismic data associated with changes in acquisition geometry, variable source coupling, and daily/ seasonal variations in the near surface. We developed these results with a synthetic case study using a realistic 1D elastic model with a free surface and acquisition geometry from an actual field experiment conducted in Saudi Arabia. © 2015 Society of Exploration Geophysicists.
Zheng J.,China University of Mining and Technology |
Zheng J.,Lawrence Berkeley National Laboratory |
Zheng L.,Lawrence Berkeley National Laboratory |
Liu H.-H.,Aramco Research Center |
And 2 more authors.
International Journal of Rock Mechanics and Mining Sciences | Year: 2015
As the effective stress increases, low-permeability rock undergoes fairly small porosity changes, but significant decrease in the permeability. Empirical relationships based on laboratory-measured data, typically exponential or power laws, have been proposed to describe the stress-permeability, stress-porosity, and permeability-porosity relationships. However, these approximations yield poor fitting in low effective stress ranges, or unreasonable prediction for certain effective stresses. In this study, we develop a series of theoretical models for the essential relationships among the porosity, permeability and the effective stresses for low-permeability sedimentary rock, based on the concept of Two-Part Hooke's Model (TPHM). The TPHM conceptualizes an intact rock into a soft part and a hard part, which comply with the natural-strain-based and engineering-strain-based Hooke's law, respectively. The derived relationships are validated by the experimental data from the literature. The comparisons show that the theoretical predictions agree well with the experimental results. The soft-part, comprising of only a small portion of the rock body, is responsible for the significant permeability reduction in low stress levels. The high stress-sensitivity of permeability is mainly attributed to the micro-crack (soft-part) closure in the intact rock. © 2015 Elsevier Ltd.
Pei Y.,Argonne National Laboratory |
Pei Y.,Aramco Research Center |
Hu B.,Cummins Inc. |
Som S.,Argonne National Laboratory
Journal of Energy Resources Technology, Transactions of the ASME | Year: 2016
An n-dodecane spray flame was simulated using a dynamic structure large-eddy simulation (LES) model coupled with a detailed chemistry combustion model to understand the ignition processes and the quasi-steady state flame structures. This study focuses on the effect of different ambient oxygen concentrations, 13%, 15%, and 21%, at an ambient temperature of 900 K and an ambient density of 22.8 kg/m3, which are typical diesel-engine relevant conditions with different levels of exhaust gas recirculation (EGR). The liquid spray was treated with a traditional Lagrangian method. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. It is observed that the main ignitions occur in rich mixture, and the flames are thickened around 35-40 mm off the spray axis due to the enhanced turbulence induced by the strong recirculation upstream, just behind the head of the flames at different oxygen concentrations. At 1 ms after the start of injection (SOI), the soot production is dominated by the broader region of high temperature in rich mixture instead of the stronger oxidation of the high peak temperature. Multiple realizations were performed for the 15% O2 condition to understand the realization-to-realization variation and to establish best practices for ensemble-averaging diesel spray flames. Two indexes are defined. The structure-similarity index (SSI) analysis suggests that at least 5 realizations are needed to obtain 99% similarity for mixture fraction if the average of 16 realizations is used as the target at 0.8 ms. However, this scenario may be different for different scalars of interest. It is found that 6 realizations would be enough to reach 99% of similarity for temperature, while 8 and 14 realizations are required to achieve 99% similarity for soot and OH mass fraction, respectively. Similar findings are noticed at 1 ms. More realizations are needed for the magnitude-similarity index (MSI) for the similar level of similarity as the SSI. Copyright © 2016 by ASME.
Deng Z.J.,Massachusetts Institute of Technology |
Morton S.W.,Massachusetts Institute of Technology |
Bonner D.K.,Massachusetts Institute of Technology |
Gu L.,Massachusetts Institute of Technology |
And 2 more authors.
Biomaterials | Year: 2015
An important aspect in the design of nanomaterials for delivery is an understanding of its uptake and ultimate release to the cytosol of target cells. Real-time chemical sensing using a nanoparticle-based platform affords exquisite insight into the trafficking of materials and their cargo into cells. This versatile and tunable technology provides a powerful tool to probe the mechanism of cellular entry and cytosolic delivery of a variety of materials, allowing for a simple and convenient means to screen materials towards efficient delivery of therapeutics such as nucleic acids. © 2015 Elsevier Ltd.
Hu R.,Wuhan University |
Chen Y.-F.,Wuhan University |
Zhou C.-B.,Wuhan University |
Zhou C.-B.,Nanchang University |
Liu H.-H.,Aramco Research Center
Acta Geotechnica | Year: 2016
This paper proposed a numerical formulation for unsaturated flow problems with nonlinear boundaries of seepage face and soil–atmosphere interface via the concept of parabolic variational inequality (PVI) method. A unified unilateral boundary condition was first proposed to represent the conditions on the seepage face and soil–atmosphere interface boundaries within the partial differential equation (PDE) formulation. A PVI formulation mathematically equivalent to the PDE formulation was then proposed, which automatically transforms the flux part of the unified unilateral boundary condition into the natural boundary condition and eliminates the singularity at seepage points. By discretizing the PVI formulation, a finite element procedure together with an iterative algorithm was suggested. An existing experiment of unsaturated flow in a layered hillside and a laboratory test of unsaturated flow through sand flume performed in this study were used to validate the proposed method, with a good agreement between the measured and computed results and a satisfactory balance of mass being maintained during the simulations. The numerical results also indicated that the problem of mesh dependence associated with unsaturated flow simulations is well addressed with the proposed numerical method. Finally, the process of unsaturated flow in a soil slope with layers of horizontal drains subjected to rainfall/evaporation was further examined. The numerical results reveal that the deployment of drains in a soil slope can significantly lower the pore water pressure around the drains, with the bottom layer drains being most effective in controlling the seepage flow. © 2016 Springer-Verlag Berlin Heidelberg